Network security consists of the provisions and policies adopted by a network administrator to prevent and monitor unauthorized access, misuse, modification, or denial of a computer network and network-accessible resources.

Network security involves the authorization of access to data in a network, which is controlled by the network administrator. Users choose or are assigned an ID and password or other authenticating information that allows them access to information and programs within their authority. Network security covers a variety of computer networks, both public and private, that are used in everyday jobs conducting transactions and communications among businesses, government agencies and individuals. Networks can be private, such as within a company, and others which might be open to public access.

Network security is involved in organizations, enterprises, and other types of institutions. It does as its title explains: It secures the network, as well as protecting and overseeing operations being done. The most common and simple way of protecting a network resource is by assigning it a unique name and a corresponding password.

There are several ways to provide security within a network and between different networks and clients. Everything from the data sent over the network to the actual use and accessibility of the network can be controlled and secured.

Secure Transmission

Providing secure transmission of data is similar to using a courier to bring a valuable and sensitive document from one person to another. When the courier arrives at the sender, he would normally be asked to prove his identity.

Once this is done, the sender would decide if the courier is the one he claims to be, and if he can be trusted. If everything seems to be correct, the locked and sealed briefcase would be handed over to the courier, and he would deliver it to the recipient. At the receiver's end, the same identification procedure would take place, and the seal would be verified as "unbroken". Once the courier is gone, the receiver would unlock the briefcase and take out the document to read it.

A secure communication is created in the same way, and is divided into three different steps:

1. Authentication
2. Authorization
3. Privacy

Authentication

This initial step is for the user or device to identify itself to the network and the remote end. This is done by providing some kind of identity to the network/system, like a username and password, an X509 (SSL) certificate, and using the 802.1x standard.

A closer look at IEEE 802.1x authentication

Pushed by the wireless community looking for stronger security methods, the 802.1x standard is among the most popular authentication methods in use today: IEEE 802.1X provides authentication to devices attached to a LAN port, establishing a point-to-point connection or preventing access from that port if authentication fails.

How it works

Clients and servers in an 802.1x network authenticate each other with the help of digital certificates provided by a Certification Authority. These are then validated by a third-party entity, such as an authentication server called a RADIUS server, one example of which is Microsoft Internet Authentication Service.

Authorization

The next step is to have this authentication authorized and accepted, that is verifying whether the device is the one it claims to be. This is done by verifying the provided identity within a database or list of correct and approved identities. Once the authorization is completed, the device is fully connected and operational in the system

Privacy

The final step is to apply the level of privacy required. This is done by encrypting the communication, which prevents others from using/reading the data. The use of encryption could substantially decrease performance, depending on the implementation and encryption used.

Privacy can be achieved in several ways. Two commonly used methods are:

1. VPN (Virtual Private Network)
2. HTTP over SSL/TLS (also known as HTTPS)

VPN (Virtual Private Network)

A VPN creates a secure tunnel between the points within the VPN. Only devices with the correct "key" will be able to work within the VPN. Network devices between the client and the server will not be able to access or view the data. With a VPN, different sites can be connected together over the Internet in a safe and secure way.

HTTP over SSL/TLS

Another way to accomplish security is to apply encryption to the application data itself. In this case, there is no secure tunnel as with the VPN solution, but the actual application data sent is secured. There are several different encryption protocols available, for example SSL/TLS. When using HTTP over SSL/TLS, the device or computer will install a certificate into the unit, which can be issued locally by the user or by a third-party such as Verisign. In most cases when a connection between two devices is established, the certificate of the server will be verified by the client and, if trusted, an encrypted communication is opened. When creating a secure connection to Web sites such as Internet banks, the certificates of the two units will be verified. When you see "https://…" in the Web address, the "s" stands for secure and it means that you are requesting a secure connection.

Protecting Single Devices

Security also means protecting single devices against intrusions, such as unauthorized users trying to gain access to the unit, or viruses and similar unwanted items. 

Access to PCs or other servers can be secured with user names and passwords, which should be at least 6 characters long (the longer the better), combining numbers and figures (mixing lower and upper cases). In the case of a PC, tools like finger scanners and smart cards can also be used to increase security and speed up the login process.

To secure a device against viruses, worms and other unwanted items, a virus scanner of good quality with up-to-date filters is recommended. This should be installed on all computers. Operating systems should be regularly updated with service packs and fixes from the manufacturer. When connecting a LAN to the Internet, it is important to use a firewall. This serves as a gatekeeper, blocking or restricting traffic to and from the Internet. It can also be used to filter information passing the firewall or to restrict access to certain remote sites.